Ammonium salt containing waste waters strongly favors the growth of algae in rivers and lakes and thereby reduces their oxygen content, while ammonia containing waste waters are highly toxic to fish. These types of waste waters cannot be discharged untreated into public waters.
Various methods are known for destroying the ammonium ion. However, these processes on the one hand are much too expensive industrially or for other reasons cannot be carried out on a large scale.
According to a well known method which also is used in practice to protect the environment, ammonium ions are converted to nitrogen by oxidation. The industrial oxidizing agent is chlorine which, among others, is used in the form of bleaching liquor or chloride of lime.
The amounts of chlorine added to be sure are high, the excess over the theoretical amount according to the equation EQU 2 NH.sub.4 Cl + 3NaOCl .fwdarw. N.sub.2 + 3NaCl + 2HCl + 3H.sub.2 O (I)
can amount to a multiple and even up to six times the theoretical amount, see Chem. Abst. 80 (1974) 63490g.
The complicated reaction of ammonia or ammonium ion with chlorine has been investigated many times, see Gmelin, 8th edition System No. 5 pages 285-286, as well as 490 and 497 wherein additional ideas on the manner of action of chlorine are discussed.
It is only certain that depending on the pH the 3 chloramines, namely, mono- and dichloramine and the explosive nitrogen trichloride appear during this reaction.
The exact limits given in the literature for the pH and the existence of the individual chloramines, see Chem. Abst. 48 (1954) 5705g, indeed are generally correct, i.e., if the same pH prevails in the entire reaction medium provided that the course of the reaction proceeds slowly enough. If this is not possible, however, and local pH differences occur, there can also be formed in a reaction medium having a high pH nitrogen trichloride which normally only exists at low pH. Because of the danger of explosion with nitrogen trichloride and its undesirable effects on the environment this makes it impossible to purify ammonia or ammonium salt containing waste water with chlorine or its compounds such as alkali or alkaline earth hypochlorites.
In Bishop U.S. Pat. No. 3,733,266 it is proposed to react chlorine with ammonia to form nitrogen and hydrochloric acid at a pH of 5.8 to 9.5, preferably in the range of 6-8. The equation for the reaction as shown on col. 3 last line is EQU 3Cl.sub.2 + 2NH.sub.3 .fwdarw. N.sub.2 + 6HCl
It is stated that there is used a Cl:NH.sub.3 --N weight ratio of about 8-10:1. This is above a chlorine atom to ammonia molecule ratio of 3:1. Bishop uses chlorine and a base such as sodium, potassium or calcium hydroxide to supply the chlorine and necessary pH. In place of these two materials Bishop can employ sodium hypochlorite, col. 5 lines 53-70.
It is important--according to the Bishop process--that the chloramines being still present after finishing the reaction can only be removed by an additional absorption stage with activated carbon.
The reaction between chlorine and ammonia to form nitrogen is therefore not quantitative.
The purpose of the present invention is to develop a process for the quantitative purification of waste water containing ammonia or ammonium salts without the formation of nitrogen trichloride.